During human evolution, which paired change occurred with brain enlargement?

During human evolution, which paired change occurred with brain enlargement?

• A. The gut became 60% smaller.
• B. The gut became 60% larger.
• C. The liver enlarged.
• D. The lungs reduced in size.

Answer: (A)

The main idea is an energy budget trade-off: brain enlargement in human evolution required a huge input of energy, and the digestive system is one of the most energy-demanding tissues. To free up calories for a bigger brain, the digestive tract could become relatively smaller. In humans, the gut is substantially smaller than expected for our body size compared with other primates, which fits the idea that dietary shifts—such as eating more energy-dense foods like meat and, later, using cooking—raised energy availability. Reducing gut size by a large margin (often described as a substantial reduction, around 60%) would help redirect energy toward brain growth, supporting the enlargement of the brain over time. Other options don’t align as neatly with this energetic reallocation; a larger gut would actually consume more energy and hinder brain growth, and changes to the liver or lungs don’t connect as directly to the brain’s energetic demands in the same way.

The main idea is an energy budget trade-off: brain enlargement in human evolution required a huge input of energy, and the digestive system is one of the most energy-demanding tissues. To free up calories for a bigger brain, the digestive tract could become relatively smaller. In humans, the gut is substantially smaller than expected for our body size compared with other primates, which fits the idea that dietary shifts—such as eating more energy-dense foods like meat and, later, using cooking—raised energy availability. Reducing gut size by a large margin (often described as a substantial reduction, around 60%) would help redirect energy toward brain growth, supporting the enlargement of the brain over time. Other options don’t align as neatly with this energetic reallocation; a larger gut would actually consume more energy and hinder brain growth, and changes to the liver or lungs don’t connect as directly to the brain’s energetic demands in the same way.